U01B9Lost Communication With Switch Input Module C
- Generic OBD-II code · Network
- How the car detects it
- Module C is the third switch input module. Such units often hang off a sub-bus: a Yazaki patent on door electronics shows a door unit that takes commands from CAN and forwards them over a LIN sub-bus to local nodes such as switches, window lift and mirror. When module C drops off, the receiver logs U01B9 and normally treats the affected switch states as released, a safe default. No manufacturer documents this code publicly, so only the vehicle's own wiring diagram reveals which buttons and which bus segment belong to C. Because only operating elements are concerned, the MIL stays off. A wire broken where the harness moves, at a door hinge, seat rail or steering column, is a likely cause. U04BC handles invalid content from C.
- What you may notice
- Buttons served by module C ignored
- Fault appears or disappears when moving a door, seat or the steering wheel
- Likely causes
- LikelyWire broken in a moving harness section (door hinge, seat rail, steering column)
- PossibleFault in the unit that hosts the sub-bus of module C
- RareSwitch input module C faulty
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.